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Measurements of moisture production caused by various sources
Energy and Buildings 127 (2016) 884–891
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Measurements of moisture production caused by various sources Jurgis Zemitis ∗ , Anatolijs Borodinecs, Marta Frolova Heat, Gas and Water technology institute, Riga Technical University, Kipsalas street 6B/6A, LV-1048, Riga, Latvia
a r t i c l e
i n f o
Article history: Received 1 January 2016 Received in revised form 14 June 2016 Accepted 15 June 2016 Available online 19 June 2016 Keywords: Moisture production Cloth drying Plants Humans Relative humidity
a b s t r a c t To accurately predict indoor air moisture levels, the input data that includes the moisture production must be determined with high accuracy. The existing researches provide data about the estimated moisture generation rate by household activities but the data vary largely between the publications. Therefore, during this research, measurements of moisture generation from sources like cloth washing, emission by plants and human respiratory process were carried out. The moisture production in case of natural cloth washing and drying in indoors was performed in household environment at different mechanical washing machine drying revolution speeds and for five pieces of typical clothes. Also the influence of mechanical washing machine drying revolution speed as well as clothing fabric was determined. The moisture production from plants and humans was measured in climatic chamber with controlled environment by calculating it according to measured relative humidity. The overall results showed inconsistency with the ones provided in existing researches. The obtained moisture production values were lower for each of the source. This findings can be applied in future calculations when predicting indoor humidity. © 2016 Elsevier B.V. All rights reserved.
1. Introduction The indoor relative humidity can have large effect on both human health [13] as well as building materials [11]; therefore, it is important to control it in predetermined boundaries. To do this, it is necessary to predict the RH during design stage. For this task the sources of humidity must be correctly assumed. In general, there are several processes in household activities that generate moisture. Some of these include moisture generation from peoples due to respiratory process, moisture by preparing dishes, dish-washing, bathing or showering, cloth washing, and cloth drying. All these must be taken into account to precisely predict the indoor relative humidity. The moisture generation can be given for whole residential buildings like presented by TenWolde and Walker [15]. They account for several factors – the number of people in the family, their habits, building equipment, what type of cloth drying is used, plants, etc. Another approach is to calculate moisture generation by each source and sum them afterwards. Moisture content, which is released from the people, depends on the working load, air temperature, as well as individual metabolic profile. The moisture generation by persons has been noted and reported for a long period, but different sources provide different
∗ Corresponding author. E-mail address: [email protected] (J. Zemitis). http://dx.doi.org/10.1016/j.enbuild.2016.06.045 0378-7788/© 2016 Elsevier B.V. All rights reserved.
results. According to a report [7], a family of four persons generates 0.20 kg/h of moisture at night and 0.21 kg/h during the day if there are three persons at home with a higher activity level. The same numbers are provided by Angell and Olson [2], while the IEA [9] quotes moisture release rates from 30 to 300 g/h per person, depending on level of activity. Values by Sanders [12] are in smaller range, as moisture generation by respiration is given from 0.9 to 1.25 kg/day which corresponds to 37.5–52.0 g/h. A bit different approach is mentioned in the Ref. [3] as it determines the moisture load by perspiration for men as loss in body weight. According to this source, at 21.1 ◦ C, a man at rest loses about 90 g/h and at work loses 270 g/h. However for more accurate estimation the moisture release must be divided in two parts – by respiration and transpiration, and the surrounding air temperature and relative humidity. According to McCutchan and Taylor [10] the respiration moisture generation is estimated to be close to 240 L/h per m2 of body surface area while the transpiration rates calculated by Ferguson and Martin [6] for ambient conditions of 20 ◦ C at 50% RH are in the range of 0.5–1.4 kg/day per adult person at rest. Given that the people during they stay inside the residential building for the longest period of time spend in relative peace or low activity then it can be assumed that a person is responsible for moisture release with the sum of respiration and transpiration processes in the range of 0.8–1.7 kg/day or approximately 30–70 g/h according to existing researches. Similar values are presented in Ref. [4] which state that a person emits 40 g/h when sleeping and 55 g/h when active. In
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Moisture production by people (g/h)
350 300 250 200 150 100 50 0
Hite, Bray Sanders 1996 British Sanders 1996 British Hite, Bray ASHRAE ASHRAE Erhorn, IEA IEA (at rest) Gertis 1986 Sourcebook standard 1948 (when (when active) standard 1948 (when 1961 (at rest) 1961 (at hard Sourcebook 1991 (at rest) 2002 (when sleeping) 2002 (when 1991 (at hard active) work) sleeping) active) work)
general it can be assumed an average a person releases 50 g/h of water vapor. Another source of moisture is indoor cloth drying. According to a source [4] due to cloth washing and drying indoors the total released moisture is estimated to be 1.5 kg/person per day. In comparison an outdated article Hite and Bray [7] reports that a load of laundry after wringing contains 11.9 of water. While Angell and Olson [2] present much lower number: 2.2–2.95 kg of water retained in a standard 3.6 kg load of laundry after dry spinning, indicating the advantages of spin dryers over wringers. Other sources for washing machine with 5 kg capacity suggest even 4.7–6.2 kg of moisture release. The number of cloth washing occurrences are dependent on the number of people in the household and their habits, in general it can be assumed that a five people household would need approximately one cloth washing process per day. According to Annex 27 [8] the frequency of cloth washing can vary from 20 times/month for 4 person household or about 5 times/week to every day. The previously mentioned research [7] also describes the water vapor release from plants. According to their experimental data a plant releases from 39 to 101 g/day as measured of seven different house plants at normal winter indoor conditions. The exact amount released by each of plants varied depending on the size and species of given plants – the larger ones released more vapor. In general the average release rate was determined to be close to 2.5 g/h by each individual plant. According to the authors, major part of this released water vapor is due to transpiration from the plant itself and only small part is due to evaporation from the soil. In comparison the [9] present a lot higher evaporation rates for potted flowers: 5–10 g/h, for potted plants: 7–15 g/h and for medium-size rubber plant: 10–20 g/h. Similar results are given by several other researchers. According to Angell [1] a plant releases around 4.1 g/h but by Erhorn and Gertis [5] a small to medium plant releases 8.3 g/h. As seen, these rates are higher if compared to the other data and are even as high as moister released by pets, therefore seem a bit unrealistic. According to Yik et al. [17], moisture release by a plant is on average about 0.84 g/h. This on the other hand is a lot lower value, but, according to TenWolde and Pilon [14], it must be adjusted for room temperature, as these measurements were done at relatively low temperatures +15 ◦ C. If this is done and we assume that the Hite and Bray did their experiments at 21.1 ◦ C, then the two rates would be very similar. According to the same publication, the water vapor release of plants is dependent on the environments relative humidity. The plant respiration increases linearly with decreasing RH until RH goes below 25% to
Moisture production by plants (g/h)
Fig. 1. Comparison of moisture production by people according to various sources.
25 20 15 10 5 0
Yik et al. 2004
Hite, Bray 1948 (small size plant)
Angell 1988
Hite, Bray 1948 (medium size plant)
IEA Sourcebook 1991 (small size plant)
Erhorn, Gertis 1986
IEA Sourcebook 1991 (medium size plant)
Fig. 2. Comparison of moisture production by plants according to various sources.
35%, as stated by experiments of West and Gaff [16]. If the relative humidity falls below 30%, then the moisture release remains constant due to closing of stomata. The existing researches provide data about the estimated moisture generation rate by these activities, but the data vary largely between the publications (see Figs. 1 and 2) and some of them might be outdated. Therefore, during this research, measurements of moisture generation from household activity like cloth washing and plants were carried out. 2. Field measurements of moisture release by cloth drying To measure the moisture generation caused by the natural drying indoors of clothes after washing them a field experiment was performed. The clothes at first were washed in electrical washing machine with different mechanical drying settings – 500, 800 and 1200 rpm. Afterwards the clothes were weighted and hanged in the apartments corridor to dry. The clothes were hanged in a freely chosen manner relatively close to each other but to make sure that they do not touch as this can influence the drying ratio. In general it was done to most naturally resemble the way in which people hang them as they do not apply scientific principles during this process. Afterwards the data of cloth weight with one hour intervals were obtained. The weighting was done on electronical scales with the maximal weighting capacity of 20 kg, precision class of 0,1 g and linearity of ±0.3 g. To determine the moisture generation and release in indoor air by cloth drying after washing with automatic cloth washer field measurements were performed. Although the existing researches have dealt with similar task, the specific of Latvia is the common practice to use household not centralized washing machines and to
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Table 1 Weight of pants before and after washing and drying at 800 rpm (g). Meas. Nr.
Before washing (g)
Directly after washing (g)
1 h later (g)
2 h later (g)
3 h later (g)
4 h later (g)
5 h later (g)
1 2 3 4 5 Average Difference
430.8 430.8 430.7 430.7 430.7 430.74 ± 0.05 217.94
685 684.2 685.1 684.6 684.5 684.68 ± 0.37
644.4 644.6 644.5 644.4 644.5 644. 48 ± 0.08
602.4 602.3 602.2 602.9 602.3 602.48 ± 0.28
555.8 555.8 555.7 556 555.8 555.82 ± 0.11
518.9 518.9 518.8 518.8 518.7 518.82 ± 0.08
504.7 504.9 504.7 504.8 504.8 504.7 ± 0.088
dry the clothes indoors. For these measurements 5 pieces of typical clothes were selected – jean type pants (98% cotton, 2% elastane), cotton underwear (95% cotton, 5% elastane), sweater (100% acryl), T-shirt (100% cotton) and suit shirt (100% cotton). Although the material for the clothes is similar, mostly cotton, it varies in the feel. While T-shirt and underwear is soft the pants and suit shirt feels more rough, dense and resistant to water. The clothes afterwards were washed inside a typical washing machine. The washing cycles ended with cloth drying in the washer by 1200, 800 or 500 rpm for initial drying. After the washing process the clothes were weighted. The weighting process was performed with one hour intervals and five measurements were done for each piece of clothing to determine the average value and to calculate the standard deviation, see example for jean type pants in Table 1. The difference in mass between each series of weighting and initial mass is considered to be caused by the additional moisture in them. Therefore it is possible to make an assumption that all this extra moisture is afterwards released inside the indoor air during the drying process. The drying took place inside a flat with indoor temperature of +22 ◦ C and relative humidity about 55%. The flat has natural ventilation with supply through constructions and windows and exhaust through natural channels in bathroom and toilet. The measured results for jean type pants showed that after the mechanical washing and drying there were still 217 g of moisture left in them. This moisture is afterwards released into the room during the natural during process. To determine the absolute moisture mass that is implemented into the room after cloth washing other types of clothes were also measured as usually one washing process involves different type of clothing. The chosen, before mentioned, clothes represent the most commonly used pieces and cover different types of fabrics. As seen from Tables 2–4 , it can be concluded that the mechanical drying intensity has large influence on the moisture content in clothes. Comparing the results of the three drying processes with 1200, 800 and 500 rpm, it can be seen that on average the relative difference in cloth weight directly after washing process is strongly dependent on it and changes from 42% to 61% to 89% respectively. The difference is up to two times if comparing cloth weight coming out of washing machine after 1200 and 500 rpm drying. It must be noted that not all of the cloth pieces were exactly the same in the tests, for some of them only the clothing type was identical while the exact model and fabric varied. However analysing the results also for the exact same clothes, like underwear, the results showed that at 500 rpm drying process the increase in weight was 112% while at 800 revolutions 85%. The Table 3 shows the difference in weight and drying rate for five pieces of clothes at an average mechanical drying rate – 800 rpm. It can be seen that mass increase of all clothes directly after washing and mechanical drying to before washing is about 717 g. This accounts for relative increase in weight of 61%. However the increase strongly varies depending on fabric and type of clothes and is in range from 50% up to 90%. The largest increase in weight is for T-shirt and smallest for sweater. Similar results can be seen in Table 2 and 4, and shows that independently of dryer’s rotation speed the T-shirt always is the one, which is dried out the
least with the underwear being the close second. It can lead to conclusion that the clothes that are initially smaller and lighter as well as are made of soft cotton type material have the largest increase in mass expressed in percentage to their own weight. All the extra moisture that clothes contain after the washing and mechanical drying process is released to indoor air during natural drying process of clothing. The Table 5 shows the data of cloth mass with 1 h intervals in case when they are dried at 800 rpm. These results, as well as data about cloth natural drying after mechanical drying at analyzed revelations is shown in Fig. 3. This following figure shows natural drying process as function of time and it can be seen that the drying process generally follows logarithmical scale. Both after 5 h and 7 h drying there was still around 100 g of extra moisture in clothes compared to the initial state. However not all cloth types dried at even pace. For example Fig. 4 shows the drying speed of different cloth pieces as decrease of extra weight if compared to weight before washing. It can be concluded that a more lightweight fabric clothes like sweater and shirts dry faster. They reach overweight of only 10% already after 2–3 h. At the same time jeans dry a lot slower, although they do not contain relatively as much water as T-shirt or underwear after washing process. Even after 9 h they are still more than 10% heavier than before washing. This can be explained due to their heavier fabric and the shape of pants that allow less contact with air and therefore slower evaporation. To estimate the overall moisture production due to cloth washing it is necessary to determine the total amount of clothes that a person washes each week. It could be reasonable to assume that for each day of a weak a person has different set of clothes that consist of socks, underwear, shirt or T-shirt. The pants and sweater on average could be washed about twice a week and additionally there would be some clothes for training and some rarer occurrences like bed clothes, towels, hats etc. To take that into account it would be possible to assume that additional coefficient of 100% can be used. Therefore, it is possible to calculate the moisture generated weekly by knowing the data about moisture content in these clothes assuming that the average washing machine has 800 rpm for drying. The data for this situation is given in Table 3. Therefore we can calculate the total generated moisture as follows: (7 × (65 + 177 + 150) + 2 × (254 + 123)) × 2 = 6996g or on average 999g/day,(1)
Another way of predicting the moisture generated by cloth washing would be to assume that on average a person washes clothes two times per week. Knowing that an average washing machine is intended for washing capacity of 7 kg and by applying results that on average the weight increases for about 61% per washing process it can be calculated that the total increase would be 2×(7000 × 0.61) = 8540 g or about 1220 g/day if two fully stacked washing machines are done per week. Another calculation method would be to use the existing study researches that state that a household of 4–5 people wash clothes once every day. Therefore applying the same method as above we can calculate the average moisture production per day for whole household 7×(7000 × 0.61)/7 = 4270 g/day or 1067 g/day per person if 4 persons are in the household.
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Table 2 Weight of different clothes before and after washing and drying at 1200 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
406.7 136.0 71.5 198.6 278.6 1091.4
601.8 218.5 107.3 286.7 336.7 1551
195.1 82.5 35.8 88.1 58.1 459.6
48% 61% 50% 44% 21% 42%
Table 3 Weight of different clothes before and after washing and drying at 800 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
430.74 194.42 75.62 204.5 275.1 1180.38
684.68 371.24 140 304.52 397.7 1898.14
253.94 176.82 64.38 100.02 122.6 717.76
59% 91% 85% 49% 45% 61%
Table 4 Weight of different clothes before and after washing and drying at 500 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
439.6 142.3 65 203.8 277.5 1128.2
834.8 302.5 137.7 367.8 491.4 2134.2
395.2 160.2 72.7 164 213.9 1006
90% 113% 112% 80% 77% 89%
Table 5 Weight decrease of different cloth pieces during natural drying after mechanical drying at 800 rpm (g). Directly after washing (g) Pants T-shirt Underwear Shirt Sweater Sum
684.68 371.24 140 304.52 397.7 1898.14
1 h later (g)
2 h later (g)
644.48 333.08 130.38 253.14 351.7 1712.78
3 h later (g)
602.42 303.92 121.62 228.84 318.1 1574.9
4 h later (g)
555.82 278.68 117.34 215.84 291.9 1459.58
518.82 253.24 105.64 211.96 279.4 1369.06
5 h later (g) 504.78 240.16 100.46 210.4 276.7 1332.5
2300 2100 weight, grams
1900 1700 1500 1300 1100 900 700
0
1
2
3
4
5
6
7
8
time, h drying at 500 rpm
drying at 800 rpm
drying at 1200 rpm
Fig. 3. Change in weight of clothes after automatic washing and indoor drying process.
These results are in range of the ones provided in existing literature that suggest value of 1500 g/day however they are notably lower by about one third. This could be explained by the improved mechanical drying performance of modern washing machines as well as in general it is common to assume the moisture production by various sources with extra safety factor during calculations and therefore these values in standards are given higher.
Also it must be noted that it is rather inconvenient to take this moisture generation into account during relative humidity prediction process as it is impossible to precisely determine the exact days on whom the drying would occurs and also some additional research about cloth washing habits depending on persons in household should be performed. Nevertheless this data can be used to calculate the maximal moisture generation if it is assumed
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extra weight of clothes, %
120% 100% 80% 60% 40% 20% 0% 0
1
2
3
4
5
6
7
8
9
10
Time, h Pants
T-shirt
Underwear
Shirt
Sweater
Fig. 4. Natural drying speed of different clothes after 1200 revelation mechanical drying process.
Fig. 5. Climatic chamber with three plants for moisture generation measurements.
that there would be one occurrence of drying of one fully stacked washing machine. 3. Climatic chamber measurements of moisture release from plants Another source of moisture generator in indoor environment is plants. Although their impact is a lot smaller than compared to moisture generation from humans or cloth drying it can vary depending on the number and size of plants. In some case they can actually serve as a notable source because some persons like to have large number of them either in office or house to provide nice environment. Also as it is widely known that the plants serve as CO2 reducer some offices are especially having a lot of them. The measurements of moisture generation by plants and people were performed in controlled situation in climatic chamber. The chamber has dimensions of length and width of 3.4 m and with the ceiling height of 2.3 m. The total volume therefore is 26.58 m3 . The chamber is specially constructed to perform different types of HVAC system tasks like radiant heating analysis or cooling ventilation system balancing etc. and to perform measurements of these processes. During the tests all the openings were sealed therefore making the chamber almost perfectly air tight. For the purpose of calculations the air exchange rate was assumed to be negligible as the air tightness of the climatic chamber was previously tested by tracer gas measurements. To measure the moisture generation from the plants a sample consisting of three plants was put in the climatic chamber (see Fig. 5). All the plants were average sized and before placing in
the chamber were watered. Afterwards the plants were left at the chamber for 15 days and the relative humidity as well as temperature was measured (see Fig. 6). After the data was obtained, the absolute humidity change in the climatic chamber was calculated according on the basis of measured temperature and relative humidity (see Fig. 7). To determine the actual moisture generated by the plants located in the climatic chamber the total humidity must be calculated. This is done by knowing the volume of the climatic chamber which is about 26.6 m3 and by multiplying the previously determined absolute humidity with this volume. The resulting graph would show exactly the same trend as for absolute humidity as these results are proportional. According to the results at the starting moment the absolute humidity in the chamber was 6.58 g/m3 or 175 g of total water vapor. While at the end of measuring period the humidity had risen to 9.22 g/m3 or 245.3 g. This means that on average the moisture had increased just by 4.7 g/day or, if assuming that all three plants produce the moisture on about the same rate as they are comparable in size, then one plant would account for 1.57 g/day or 0.065 g/h. To verify the test a second set of measurements were performed. During this test a total of six plants (see Fig. 8) were located in the climatic chamber and left there for five days. The plants were watered twice during the test period with about 3 L of water for all of them to simulate real life situation. The obtained results from second measurement series with six plants showed that during the 5 day period the total humidity increased by 84.2 g from 205.7 to 289.9 g. This means that on average the increase was 16.84 g/day or 0.7 g/h. If assuming that all plants are about equal than each of them would generate around 2.8 g/day or 0.12 g/h. The graph also shows that the increase in the given condition were not linear for the period of experiment. The increase in moisture content in room follows general trendline of third level polynomial equitation, with more rapid increase shortly after the plants are watered. This can be explained by the fact that the increase in air relative moisture decreases the moisture production by plants due to closing of stomata. Comparing the results to existing studies that suggest that a plant would produce moisture with rate 5–15 g/h or even according to other data 0.84 g/h which corresponds to 20.2 g/day our obtained values of 2.8 g/h are a lot lower. Our measurements provided results that are 12.8 up to 230 times lower. The cause of this difference could be explained by following factors – during our experiment the plants were not intensively watered while it is unknown was it done for other experiments; the moisture could in some way escape
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25 24.5 24 23.5 23 22.5 22 21.5 21 20.5 20
55 50
%
45 40 35 30 0
100
200
300
400
500
600
700
0C
J. Zemitis et al. / Energy and Buildings 127 (2016) 884–891
800
me, h RH, %
Temp, °C
Fig. 6. Relative humidity and temperature in climatic chamber during moisture generation by plants.
10
Absolute humidity, g/m3
9 y = 0.0073x + 6.836 R² = 0.9787
8 7 6 5 4 0
50
100
150
200
250
300
350
400
Time, h Fig. 7. Change in absolute humidity (g/m3 ) in climatic chamber due to moisture generation by three plants.
300 y = 5E-05x3 - 0.0144x2 + 1.6578x + 211.93 R² = 0.9819
Total humidity, g
280
Moment of watering
260 240
Moment of watering
220 200 180 160 0
20
40
60
80
100
120
Time, h Fig. 8. Change in total humidity (g) in climatic chamber due to moisture generation by six plants.
the climatic chamber through constructions although it should be relatively sealed, or possibly these exact plants during this period of year, which was winter, release smaller amount of moisture due to slower vegetation. Or maybe some part of the moisture was assimilated in the wall material of climatic chamber, although it should be small amount as the inside of chamber is made covered with aluminum sheets.
4. Climatic chamber measurements of moisture release from people To verify the existing information about moisture generation from people a climatic chamber measurement was performed. It took place in the same climatic chamber. During the test a single person, with slim body type and length of 1.89 cm was located in
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250
Moisture content in room, g
230 210 190 170 150 Stable increase in moisture
130 110 90 70 50 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Time, h Fig. 9. Moisture content increase in climatic chamber due to a person.
the chamber for four hours and was representing low activity level seated work and had clothing insulation of 0.9 Clo. The temperature inside the climatic chamber at the start of experiment was +22 ◦ C while at the end +24 ◦ C, and the relative humidity around 35%. After the data analysis the results were processed the same way as in case for plant moisture generation calculations. The obtained results can be seen in Fig. 9. The results show that the total moisture content increased linearly during the time of test. Although for about the first half an hour the moisture content was stable and did not change. This could maybe be explained by the fact that the room contained some objects like typical plywood material school type table and chair as well as the clothes on person. After this period the objects reached equilibrium state and the produced moisture directly influenced the air. If this is taken into assumption the actual produced moisture must be calculated starting from the one hour mark into the test. At this moment the calculated total moisture content in the room was 172.45 g while at the end of test 231.7 g. Therefore the increase in moisture during this period, which was 2 h 50 min or 2.83 h, is 59.25 g. This means that the moisture release is estimated to be 59.25/2.83 = 20.94 g/h. Comparing this to existing data that suggest that a person emits from 30 to 120 g/h with average of about 50 g/h it can be concluded that according to our test the results are 1.5 up to 5 times lower. This follows the general trend of over-exaggerated values as for moisture production from cloth drying and plants. Therefore it can be concluded that the moisture generation rates are very variable and strongly dependent on the performed type of measurements and each individual person with his metabolically rate.
5. Conclusions Measurements of indoor moisture production rates by cloth drying and from plants as well as peoples was performed. The results for indoor cloth drying indicated that this process would account for average of 1220 g/day for one person compared to 2000 g/day suggested in existing literature. However this value is dependent on the set revelations of washing machines mechanical drying process and can vary largely depending on this as well as on persons habits. The obtained results showed that the drying in washing machine can have serious impact on the cloth moisture content after the washing process. The average relative mass increase, which represents the moisture amount, can vary between 42–89% if the set RPM is 500 or 1200 respectively. Further experiments could also be performed to find correlation between cloth material and
their moisture absorbing powers as the actual experiment results showed that it is strongly dependent. The moisture generation by plants was estimated to be in range of 0.07 g/h to 0.12 g/h compared to existing researches of 0.84 up to 15 g/h for larger plants. The measurements were based on two sets, one with three plans and other six plants located in sealed climatic chamber. According to performed climatic chamber measurements a person generates about 21 g/h, while in low activity work, in comparison to 30–50 g/h stated in existing literature. In general all obtained results indicated much lower produced humidity values compared to the ones stated in literature. It can be explained by objective factors like improved mechanical drying level of modern day washing machines, different experimental setups and individual differences in peoples, plants or clothes. Also subjective factors can play important role. For example the guidebooks and standards have general tendency to overvalue the presented various constants as safety factors. However in the case of relative humidity this can play against as there is usually problems with lowered indoor RH and if the moisture sources will be overvalued the actual situation can be worse than predicted one. Therefore further experiments must be performed to correctly determine the various moisture sources. These experiments must also include moisture generation by preparing dishes, dishwashing, bathing and showering. Acknowledgment Support for this work was provided by the Riga Technical University through the Scientific Research Project Competition for Young Researchers No. ZP-2016/28. References [1] W.J. Angell, Home Moisture Sources, CD-FO-3396, University of Minnesota, St. Paul, MN: Cold Climate Housing Information Center, Minnesota Extension Service, 1988. [2] W.J. Angell, W.W. Olson, Moisture Sources Associated with Potential Damage in Cold Climate Housing CD-F0O-3405-1988, University of Minnesota, St. Paul, MN: Cold Climate Housing Information Center, Minnesota Extension Service, 1988. [3] ASHRAE, Guide and Data Book: Fundamentals and Equipment, American Society of Heating, New York, GA, 1961 (Refrigerating and Air-Conditioning Engineers). [4] BS 5250, Code of Practice for Control of Condensation in Buildings, British Standard, 2002. [5] H. Erhorn, K. Gertis, Minimal thermal insulation and minimal ventilation, Gesund. Eng. 107 (1986).
J. Zemitis et al. / Energy and Buildings 127 (2016) 884–891 [6] J.C. Ferguson, C.J. Martin, A study of skin temperatures, sweat rate and heat loss for burned patient, Clin. Phys. Physiol. Meas. 12 (4) (1991) 367–375. [7] S.C. Hite, J.L. Bray, Research in Home Humidity Control, Purdue University, Lafayette, 1948, pp. 72 (Research Series No. 106, Engineering Experiment Station). [8] Annex 27: Evaluation and demonstration of domestic ventilation system – State of Sweden, 1995. [9] IEA, International Energy Agency, Leuven, Belgium, 1991. [10] J.W. McCutchan, C.L. Taylor, Respiratory heat exchange with varying temperature and humidity of inspired air, J. Appl. Physiol. 4 (2) (1951) 121–135. ˙ V. Stankeviˇcius, Evaluation of sorption moistening in research [11] R. Miniotaite, of moisture-caused deformations of building materials, J. Civil Eng. Manage. 9 (3) (2003) 203–207. [12] C. Sanders, International Energy Agency, Leuven, Belgium, 1996. ˇ [13] L. Seduikyte, V. Paukˇstys, Evaluation of indoor environment conditions in offices located in buildings with large glazed areas, J. Civil Eng. Manage. 14 (1) (2008) 39–44.
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[14] A. TenWolde, C.L. Pilon, The effect of indoor humidity on water vapor release in homes, in: Proc. of 30 Years of Research, Thermal Performance of the Exterior Envelopes of Whole Buildings X, 2–7 December 2007. Atlanta, GA, ASHREA, 2007, pp. 1–9. [15] A. TenWolde, I. Walker, Interior moisture design loads for residences, December 2001, Atlanta, USA, in: Proc. of Performance of Exterior Envelopes of Whole Buildings VIII: Integration of Building Envelopes, 001, 2001, p. 6. [16] D.W. West, D.F. Gaff, The effect of leaf water potential, leaf temperature and light intensity on leaf diffusion resistance and the transpiration of leaves of Malus sylvestris, Physiol. Plant. 38 (2) (1976) 98–104. [17] F.W.H. Yik, P.S.K. Sat, J.L. Niu, Moisture generation through chinese household activities, Indoor Built Environ. 13 (2) (2004) 115–131.
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Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Measurements of moisture production caused by various sources Jurgis Zemitis ∗ , Anatolijs Borodinecs, Marta Frolova Heat, Gas and Water technology institute, Riga Technical University, Kipsalas street 6B/6A, LV-1048, Riga, Latvia
a r t i c l e
i n f o
Article history: Received 1 January 2016 Received in revised form 14 June 2016 Accepted 15 June 2016 Available online 19 June 2016 Keywords: Moisture production Cloth drying Plants Humans Relative humidity
a b s t r a c t To accurately predict indoor air moisture levels, the input data that includes the moisture production must be determined with high accuracy. The existing researches provide data about the estimated moisture generation rate by household activities but the data vary largely between the publications. Therefore, during this research, measurements of moisture generation from sources like cloth washing, emission by plants and human respiratory process were carried out. The moisture production in case of natural cloth washing and drying in indoors was performed in household environment at different mechanical washing machine drying revolution speeds and for five pieces of typical clothes. Also the influence of mechanical washing machine drying revolution speed as well as clothing fabric was determined. The moisture production from plants and humans was measured in climatic chamber with controlled environment by calculating it according to measured relative humidity. The overall results showed inconsistency with the ones provided in existing researches. The obtained moisture production values were lower for each of the source. This findings can be applied in future calculations when predicting indoor humidity. © 2016 Elsevier B.V. All rights reserved.
1. Introduction The indoor relative humidity can have large effect on both human health [13] as well as building materials [11]; therefore, it is important to control it in predetermined boundaries. To do this, it is necessary to predict the RH during design stage. For this task the sources of humidity must be correctly assumed. In general, there are several processes in household activities that generate moisture. Some of these include moisture generation from peoples due to respiratory process, moisture by preparing dishes, dish-washing, bathing or showering, cloth washing, and cloth drying. All these must be taken into account to precisely predict the indoor relative humidity. The moisture generation can be given for whole residential buildings like presented by TenWolde and Walker [15]. They account for several factors – the number of people in the family, their habits, building equipment, what type of cloth drying is used, plants, etc. Another approach is to calculate moisture generation by each source and sum them afterwards. Moisture content, which is released from the people, depends on the working load, air temperature, as well as individual metabolic profile. The moisture generation by persons has been noted and reported for a long period, but different sources provide different
∗ Corresponding author. E-mail address: [email protected] (J. Zemitis). http://dx.doi.org/10.1016/j.enbuild.2016.06.045 0378-7788/© 2016 Elsevier B.V. All rights reserved.
results. According to a report [7], a family of four persons generates 0.20 kg/h of moisture at night and 0.21 kg/h during the day if there are three persons at home with a higher activity level. The same numbers are provided by Angell and Olson [2], while the IEA [9] quotes moisture release rates from 30 to 300 g/h per person, depending on level of activity. Values by Sanders [12] are in smaller range, as moisture generation by respiration is given from 0.9 to 1.25 kg/day which corresponds to 37.5–52.0 g/h. A bit different approach is mentioned in the Ref. [3] as it determines the moisture load by perspiration for men as loss in body weight. According to this source, at 21.1 ◦ C, a man at rest loses about 90 g/h and at work loses 270 g/h. However for more accurate estimation the moisture release must be divided in two parts – by respiration and transpiration, and the surrounding air temperature and relative humidity. According to McCutchan and Taylor [10] the respiration moisture generation is estimated to be close to 240 L/h per m2 of body surface area while the transpiration rates calculated by Ferguson and Martin [6] for ambient conditions of 20 ◦ C at 50% RH are in the range of 0.5–1.4 kg/day per adult person at rest. Given that the people during they stay inside the residential building for the longest period of time spend in relative peace or low activity then it can be assumed that a person is responsible for moisture release with the sum of respiration and transpiration processes in the range of 0.8–1.7 kg/day or approximately 30–70 g/h according to existing researches. Similar values are presented in Ref. [4] which state that a person emits 40 g/h when sleeping and 55 g/h when active. In
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Moisture production by people (g/h)
350 300 250 200 150 100 50 0
Hite, Bray Sanders 1996 British Sanders 1996 British Hite, Bray ASHRAE ASHRAE Erhorn, IEA IEA (at rest) Gertis 1986 Sourcebook standard 1948 (when (when active) standard 1948 (when 1961 (at rest) 1961 (at hard Sourcebook 1991 (at rest) 2002 (when sleeping) 2002 (when 1991 (at hard active) work) sleeping) active) work)
general it can be assumed an average a person releases 50 g/h of water vapor. Another source of moisture is indoor cloth drying. According to a source [4] due to cloth washing and drying indoors the total released moisture is estimated to be 1.5 kg/person per day. In comparison an outdated article Hite and Bray [7] reports that a load of laundry after wringing contains 11.9 of water. While Angell and Olson [2] present much lower number: 2.2–2.95 kg of water retained in a standard 3.6 kg load of laundry after dry spinning, indicating the advantages of spin dryers over wringers. Other sources for washing machine with 5 kg capacity suggest even 4.7–6.2 kg of moisture release. The number of cloth washing occurrences are dependent on the number of people in the household and their habits, in general it can be assumed that a five people household would need approximately one cloth washing process per day. According to Annex 27 [8] the frequency of cloth washing can vary from 20 times/month for 4 person household or about 5 times/week to every day. The previously mentioned research [7] also describes the water vapor release from plants. According to their experimental data a plant releases from 39 to 101 g/day as measured of seven different house plants at normal winter indoor conditions. The exact amount released by each of plants varied depending on the size and species of given plants – the larger ones released more vapor. In general the average release rate was determined to be close to 2.5 g/h by each individual plant. According to the authors, major part of this released water vapor is due to transpiration from the plant itself and only small part is due to evaporation from the soil. In comparison the [9] present a lot higher evaporation rates for potted flowers: 5–10 g/h, for potted plants: 7–15 g/h and for medium-size rubber plant: 10–20 g/h. Similar results are given by several other researchers. According to Angell [1] a plant releases around 4.1 g/h but by Erhorn and Gertis [5] a small to medium plant releases 8.3 g/h. As seen, these rates are higher if compared to the other data and are even as high as moister released by pets, therefore seem a bit unrealistic. According to Yik et al. [17], moisture release by a plant is on average about 0.84 g/h. This on the other hand is a lot lower value, but, according to TenWolde and Pilon [14], it must be adjusted for room temperature, as these measurements were done at relatively low temperatures +15 ◦ C. If this is done and we assume that the Hite and Bray did their experiments at 21.1 ◦ C, then the two rates would be very similar. According to the same publication, the water vapor release of plants is dependent on the environments relative humidity. The plant respiration increases linearly with decreasing RH until RH goes below 25% to
Moisture production by plants (g/h)
Fig. 1. Comparison of moisture production by people according to various sources.
25 20 15 10 5 0
Yik et al. 2004
Hite, Bray 1948 (small size plant)
Angell 1988
Hite, Bray 1948 (medium size plant)
IEA Sourcebook 1991 (small size plant)
Erhorn, Gertis 1986
IEA Sourcebook 1991 (medium size plant)
Fig. 2. Comparison of moisture production by plants according to various sources.
35%, as stated by experiments of West and Gaff [16]. If the relative humidity falls below 30%, then the moisture release remains constant due to closing of stomata. The existing researches provide data about the estimated moisture generation rate by these activities, but the data vary largely between the publications (see Figs. 1 and 2) and some of them might be outdated. Therefore, during this research, measurements of moisture generation from household activity like cloth washing and plants were carried out. 2. Field measurements of moisture release by cloth drying To measure the moisture generation caused by the natural drying indoors of clothes after washing them a field experiment was performed. The clothes at first were washed in electrical washing machine with different mechanical drying settings – 500, 800 and 1200 rpm. Afterwards the clothes were weighted and hanged in the apartments corridor to dry. The clothes were hanged in a freely chosen manner relatively close to each other but to make sure that they do not touch as this can influence the drying ratio. In general it was done to most naturally resemble the way in which people hang them as they do not apply scientific principles during this process. Afterwards the data of cloth weight with one hour intervals were obtained. The weighting was done on electronical scales with the maximal weighting capacity of 20 kg, precision class of 0,1 g and linearity of ±0.3 g. To determine the moisture generation and release in indoor air by cloth drying after washing with automatic cloth washer field measurements were performed. Although the existing researches have dealt with similar task, the specific of Latvia is the common practice to use household not centralized washing machines and to
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Table 1 Weight of pants before and after washing and drying at 800 rpm (g). Meas. Nr.
Before washing (g)
Directly after washing (g)
1 h later (g)
2 h later (g)
3 h later (g)
4 h later (g)
5 h later (g)
1 2 3 4 5 Average Difference
430.8 430.8 430.7 430.7 430.7 430.74 ± 0.05 217.94
685 684.2 685.1 684.6 684.5 684.68 ± 0.37
644.4 644.6 644.5 644.4 644.5 644. 48 ± 0.08
602.4 602.3 602.2 602.9 602.3 602.48 ± 0.28
555.8 555.8 555.7 556 555.8 555.82 ± 0.11
518.9 518.9 518.8 518.8 518.7 518.82 ± 0.08
504.7 504.9 504.7 504.8 504.8 504.7 ± 0.088
dry the clothes indoors. For these measurements 5 pieces of typical clothes were selected – jean type pants (98% cotton, 2% elastane), cotton underwear (95% cotton, 5% elastane), sweater (100% acryl), T-shirt (100% cotton) and suit shirt (100% cotton). Although the material for the clothes is similar, mostly cotton, it varies in the feel. While T-shirt and underwear is soft the pants and suit shirt feels more rough, dense and resistant to water. The clothes afterwards were washed inside a typical washing machine. The washing cycles ended with cloth drying in the washer by 1200, 800 or 500 rpm for initial drying. After the washing process the clothes were weighted. The weighting process was performed with one hour intervals and five measurements were done for each piece of clothing to determine the average value and to calculate the standard deviation, see example for jean type pants in Table 1. The difference in mass between each series of weighting and initial mass is considered to be caused by the additional moisture in them. Therefore it is possible to make an assumption that all this extra moisture is afterwards released inside the indoor air during the drying process. The drying took place inside a flat with indoor temperature of +22 ◦ C and relative humidity about 55%. The flat has natural ventilation with supply through constructions and windows and exhaust through natural channels in bathroom and toilet. The measured results for jean type pants showed that after the mechanical washing and drying there were still 217 g of moisture left in them. This moisture is afterwards released into the room during the natural during process. To determine the absolute moisture mass that is implemented into the room after cloth washing other types of clothes were also measured as usually one washing process involves different type of clothing. The chosen, before mentioned, clothes represent the most commonly used pieces and cover different types of fabrics. As seen from Tables 2–4 , it can be concluded that the mechanical drying intensity has large influence on the moisture content in clothes. Comparing the results of the three drying processes with 1200, 800 and 500 rpm, it can be seen that on average the relative difference in cloth weight directly after washing process is strongly dependent on it and changes from 42% to 61% to 89% respectively. The difference is up to two times if comparing cloth weight coming out of washing machine after 1200 and 500 rpm drying. It must be noted that not all of the cloth pieces were exactly the same in the tests, for some of them only the clothing type was identical while the exact model and fabric varied. However analysing the results also for the exact same clothes, like underwear, the results showed that at 500 rpm drying process the increase in weight was 112% while at 800 revolutions 85%. The Table 3 shows the difference in weight and drying rate for five pieces of clothes at an average mechanical drying rate – 800 rpm. It can be seen that mass increase of all clothes directly after washing and mechanical drying to before washing is about 717 g. This accounts for relative increase in weight of 61%. However the increase strongly varies depending on fabric and type of clothes and is in range from 50% up to 90%. The largest increase in weight is for T-shirt and smallest for sweater. Similar results can be seen in Table 2 and 4, and shows that independently of dryer’s rotation speed the T-shirt always is the one, which is dried out the
least with the underwear being the close second. It can lead to conclusion that the clothes that are initially smaller and lighter as well as are made of soft cotton type material have the largest increase in mass expressed in percentage to their own weight. All the extra moisture that clothes contain after the washing and mechanical drying process is released to indoor air during natural drying process of clothing. The Table 5 shows the data of cloth mass with 1 h intervals in case when they are dried at 800 rpm. These results, as well as data about cloth natural drying after mechanical drying at analyzed revelations is shown in Fig. 3. This following figure shows natural drying process as function of time and it can be seen that the drying process generally follows logarithmical scale. Both after 5 h and 7 h drying there was still around 100 g of extra moisture in clothes compared to the initial state. However not all cloth types dried at even pace. For example Fig. 4 shows the drying speed of different cloth pieces as decrease of extra weight if compared to weight before washing. It can be concluded that a more lightweight fabric clothes like sweater and shirts dry faster. They reach overweight of only 10% already after 2–3 h. At the same time jeans dry a lot slower, although they do not contain relatively as much water as T-shirt or underwear after washing process. Even after 9 h they are still more than 10% heavier than before washing. This can be explained due to their heavier fabric and the shape of pants that allow less contact with air and therefore slower evaporation. To estimate the overall moisture production due to cloth washing it is necessary to determine the total amount of clothes that a person washes each week. It could be reasonable to assume that for each day of a weak a person has different set of clothes that consist of socks, underwear, shirt or T-shirt. The pants and sweater on average could be washed about twice a week and additionally there would be some clothes for training and some rarer occurrences like bed clothes, towels, hats etc. To take that into account it would be possible to assume that additional coefficient of 100% can be used. Therefore, it is possible to calculate the moisture generated weekly by knowing the data about moisture content in these clothes assuming that the average washing machine has 800 rpm for drying. The data for this situation is given in Table 3. Therefore we can calculate the total generated moisture as follows: (7 × (65 + 177 + 150) + 2 × (254 + 123)) × 2 = 6996g or on average 999g/day,(1)
Another way of predicting the moisture generated by cloth washing would be to assume that on average a person washes clothes two times per week. Knowing that an average washing machine is intended for washing capacity of 7 kg and by applying results that on average the weight increases for about 61% per washing process it can be calculated that the total increase would be 2×(7000 × 0.61) = 8540 g or about 1220 g/day if two fully stacked washing machines are done per week. Another calculation method would be to use the existing study researches that state that a household of 4–5 people wash clothes once every day. Therefore applying the same method as above we can calculate the average moisture production per day for whole household 7×(7000 × 0.61)/7 = 4270 g/day or 1067 g/day per person if 4 persons are in the household.
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Table 2 Weight of different clothes before and after washing and drying at 1200 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
406.7 136.0 71.5 198.6 278.6 1091.4
601.8 218.5 107.3 286.7 336.7 1551
195.1 82.5 35.8 88.1 58.1 459.6
48% 61% 50% 44% 21% 42%
Table 3 Weight of different clothes before and after washing and drying at 800 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
430.74 194.42 75.62 204.5 275.1 1180.38
684.68 371.24 140 304.52 397.7 1898.14
253.94 176.82 64.38 100.02 122.6 717.76
59% 91% 85% 49% 45% 61%
Table 4 Weight of different clothes before and after washing and drying at 500 rpm (g).
Pants T-shirt Underwear Shirt Sweater Sum
Before washing (g)
Directly after washing (g)
Absolute difference (g)
Relative difference (%)
439.6 142.3 65 203.8 277.5 1128.2
834.8 302.5 137.7 367.8 491.4 2134.2
395.2 160.2 72.7 164 213.9 1006
90% 113% 112% 80% 77% 89%
Table 5 Weight decrease of different cloth pieces during natural drying after mechanical drying at 800 rpm (g). Directly after washing (g) Pants T-shirt Underwear Shirt Sweater Sum
684.68 371.24 140 304.52 397.7 1898.14
1 h later (g)
2 h later (g)
644.48 333.08 130.38 253.14 351.7 1712.78
3 h later (g)
602.42 303.92 121.62 228.84 318.1 1574.9
4 h later (g)
555.82 278.68 117.34 215.84 291.9 1459.58
518.82 253.24 105.64 211.96 279.4 1369.06
5 h later (g) 504.78 240.16 100.46 210.4 276.7 1332.5
2300 2100 weight, grams
1900 1700 1500 1300 1100 900 700
0
1
2
3
4
5
6
7
8
time, h drying at 500 rpm
drying at 800 rpm
drying at 1200 rpm
Fig. 3. Change in weight of clothes after automatic washing and indoor drying process.
These results are in range of the ones provided in existing literature that suggest value of 1500 g/day however they are notably lower by about one third. This could be explained by the improved mechanical drying performance of modern washing machines as well as in general it is common to assume the moisture production by various sources with extra safety factor during calculations and therefore these values in standards are given higher.
Also it must be noted that it is rather inconvenient to take this moisture generation into account during relative humidity prediction process as it is impossible to precisely determine the exact days on whom the drying would occurs and also some additional research about cloth washing habits depending on persons in household should be performed. Nevertheless this data can be used to calculate the maximal moisture generation if it is assumed
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extra weight of clothes, %
120% 100% 80% 60% 40% 20% 0% 0
1
2
3
4
5
6
7
8
9
10
Time, h Pants
T-shirt
Underwear
Shirt
Sweater
Fig. 4. Natural drying speed of different clothes after 1200 revelation mechanical drying process.
Fig. 5. Climatic chamber with three plants for moisture generation measurements.
that there would be one occurrence of drying of one fully stacked washing machine. 3. Climatic chamber measurements of moisture release from plants Another source of moisture generator in indoor environment is plants. Although their impact is a lot smaller than compared to moisture generation from humans or cloth drying it can vary depending on the number and size of plants. In some case they can actually serve as a notable source because some persons like to have large number of them either in office or house to provide nice environment. Also as it is widely known that the plants serve as CO2 reducer some offices are especially having a lot of them. The measurements of moisture generation by plants and people were performed in controlled situation in climatic chamber. The chamber has dimensions of length and width of 3.4 m and with the ceiling height of 2.3 m. The total volume therefore is 26.58 m3 . The chamber is specially constructed to perform different types of HVAC system tasks like radiant heating analysis or cooling ventilation system balancing etc. and to perform measurements of these processes. During the tests all the openings were sealed therefore making the chamber almost perfectly air tight. For the purpose of calculations the air exchange rate was assumed to be negligible as the air tightness of the climatic chamber was previously tested by tracer gas measurements. To measure the moisture generation from the plants a sample consisting of three plants was put in the climatic chamber (see Fig. 5). All the plants were average sized and before placing in
the chamber were watered. Afterwards the plants were left at the chamber for 15 days and the relative humidity as well as temperature was measured (see Fig. 6). After the data was obtained, the absolute humidity change in the climatic chamber was calculated according on the basis of measured temperature and relative humidity (see Fig. 7). To determine the actual moisture generated by the plants located in the climatic chamber the total humidity must be calculated. This is done by knowing the volume of the climatic chamber which is about 26.6 m3 and by multiplying the previously determined absolute humidity with this volume. The resulting graph would show exactly the same trend as for absolute humidity as these results are proportional. According to the results at the starting moment the absolute humidity in the chamber was 6.58 g/m3 or 175 g of total water vapor. While at the end of measuring period the humidity had risen to 9.22 g/m3 or 245.3 g. This means that on average the moisture had increased just by 4.7 g/day or, if assuming that all three plants produce the moisture on about the same rate as they are comparable in size, then one plant would account for 1.57 g/day or 0.065 g/h. To verify the test a second set of measurements were performed. During this test a total of six plants (see Fig. 8) were located in the climatic chamber and left there for five days. The plants were watered twice during the test period with about 3 L of water for all of them to simulate real life situation. The obtained results from second measurement series with six plants showed that during the 5 day period the total humidity increased by 84.2 g from 205.7 to 289.9 g. This means that on average the increase was 16.84 g/day or 0.7 g/h. If assuming that all plants are about equal than each of them would generate around 2.8 g/day or 0.12 g/h. The graph also shows that the increase in the given condition were not linear for the period of experiment. The increase in moisture content in room follows general trendline of third level polynomial equitation, with more rapid increase shortly after the plants are watered. This can be explained by the fact that the increase in air relative moisture decreases the moisture production by plants due to closing of stomata. Comparing the results to existing studies that suggest that a plant would produce moisture with rate 5–15 g/h or even according to other data 0.84 g/h which corresponds to 20.2 g/day our obtained values of 2.8 g/h are a lot lower. Our measurements provided results that are 12.8 up to 230 times lower. The cause of this difference could be explained by following factors – during our experiment the plants were not intensively watered while it is unknown was it done for other experiments; the moisture could in some way escape
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25 24.5 24 23.5 23 22.5 22 21.5 21 20.5 20
55 50
%
45 40 35 30 0
100
200
300
400
500
600
700
0C
J. Zemitis et al. / Energy and Buildings 127 (2016) 884–891
800
me, h RH, %
Temp, °C
Fig. 6. Relative humidity and temperature in climatic chamber during moisture generation by plants.
10
Absolute humidity, g/m3
9 y = 0.0073x + 6.836 R² = 0.9787
8 7 6 5 4 0
50
100
150
200
250
300
350
400
Time, h Fig. 7. Change in absolute humidity (g/m3 ) in climatic chamber due to moisture generation by three plants.
300 y = 5E-05x3 - 0.0144x2 + 1.6578x + 211.93 R² = 0.9819
Total humidity, g
280
Moment of watering
260 240
Moment of watering
220 200 180 160 0
20
40
60
80
100
120
Time, h Fig. 8. Change in total humidity (g) in climatic chamber due to moisture generation by six plants.
the climatic chamber through constructions although it should be relatively sealed, or possibly these exact plants during this period of year, which was winter, release smaller amount of moisture due to slower vegetation. Or maybe some part of the moisture was assimilated in the wall material of climatic chamber, although it should be small amount as the inside of chamber is made covered with aluminum sheets.
4. Climatic chamber measurements of moisture release from people To verify the existing information about moisture generation from people a climatic chamber measurement was performed. It took place in the same climatic chamber. During the test a single person, with slim body type and length of 1.89 cm was located in
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250
Moisture content in room, g
230 210 190 170 150 Stable increase in moisture
130 110 90 70 50 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Time, h Fig. 9. Moisture content increase in climatic chamber due to a person.
the chamber for four hours and was representing low activity level seated work and had clothing insulation of 0.9 Clo. The temperature inside the climatic chamber at the start of experiment was +22 ◦ C while at the end +24 ◦ C, and the relative humidity around 35%. After the data analysis the results were processed the same way as in case for plant moisture generation calculations. The obtained results can be seen in Fig. 9. The results show that the total moisture content increased linearly during the time of test. Although for about the first half an hour the moisture content was stable and did not change. This could maybe be explained by the fact that the room contained some objects like typical plywood material school type table and chair as well as the clothes on person. After this period the objects reached equilibrium state and the produced moisture directly influenced the air. If this is taken into assumption the actual produced moisture must be calculated starting from the one hour mark into the test. At this moment the calculated total moisture content in the room was 172.45 g while at the end of test 231.7 g. Therefore the increase in moisture during this period, which was 2 h 50 min or 2.83 h, is 59.25 g. This means that the moisture release is estimated to be 59.25/2.83 = 20.94 g/h. Comparing this to existing data that suggest that a person emits from 30 to 120 g/h with average of about 50 g/h it can be concluded that according to our test the results are 1.5 up to 5 times lower. This follows the general trend of over-exaggerated values as for moisture production from cloth drying and plants. Therefore it can be concluded that the moisture generation rates are very variable and strongly dependent on the performed type of measurements and each individual person with his metabolically rate.
5. Conclusions Measurements of indoor moisture production rates by cloth drying and from plants as well as peoples was performed. The results for indoor cloth drying indicated that this process would account for average of 1220 g/day for one person compared to 2000 g/day suggested in existing literature. However this value is dependent on the set revelations of washing machines mechanical drying process and can vary largely depending on this as well as on persons habits. The obtained results showed that the drying in washing machine can have serious impact on the cloth moisture content after the washing process. The average relative mass increase, which represents the moisture amount, can vary between 42–89% if the set RPM is 500 or 1200 respectively. Further experiments could also be performed to find correlation between cloth material and
their moisture absorbing powers as the actual experiment results showed that it is strongly dependent. The moisture generation by plants was estimated to be in range of 0.07 g/h to 0.12 g/h compared to existing researches of 0.84 up to 15 g/h for larger plants. The measurements were based on two sets, one with three plans and other six plants located in sealed climatic chamber. According to performed climatic chamber measurements a person generates about 21 g/h, while in low activity work, in comparison to 30–50 g/h stated in existing literature. In general all obtained results indicated much lower produced humidity values compared to the ones stated in literature. It can be explained by objective factors like improved mechanical drying level of modern day washing machines, different experimental setups and individual differences in peoples, plants or clothes. Also subjective factors can play important role. For example the guidebooks and standards have general tendency to overvalue the presented various constants as safety factors. However in the case of relative humidity this can play against as there is usually problems with lowered indoor RH and if the moisture sources will be overvalued the actual situation can be worse than predicted one. Therefore further experiments must be performed to correctly determine the various moisture sources. These experiments must also include moisture generation by preparing dishes, dishwashing, bathing and showering. Acknowledgment Support for this work was provided by the Riga Technical University through the Scientific Research Project Competition for Young Researchers No. ZP-2016/28. References [1] W.J. Angell, Home Moisture Sources, CD-FO-3396, University of Minnesota, St. Paul, MN: Cold Climate Housing Information Center, Minnesota Extension Service, 1988. [2] W.J. Angell, W.W. Olson, Moisture Sources Associated with Potential Damage in Cold Climate Housing CD-F0O-3405-1988, University of Minnesota, St. Paul, MN: Cold Climate Housing Information Center, Minnesota Extension Service, 1988. [3] ASHRAE, Guide and Data Book: Fundamentals and Equipment, American Society of Heating, New York, GA, 1961 (Refrigerating and Air-Conditioning Engineers). [4] BS 5250, Code of Practice for Control of Condensation in Buildings, British Standard, 2002. [5] H. Erhorn, K. Gertis, Minimal thermal insulation and minimal ventilation, Gesund. Eng. 107 (1986).
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